The invention relates to a method and an apparatus for cleaning from the outer surface of an endless transport belt the ink, not ejected for printing purposes, of an inkjet printer.
A cleaning apparatus is known from European patent application 0 744 301 A1 for an endless transport belt in an inkjet printer, in which the presence of ink on the transport belt is detected by sensors arranged on both sides of the belt immediately following the inkjet print head. Before cleaning, the printing material printed on the transport belt is passed through a microwave drying station to dry the ink on the printing material. The drying station is followed by two ink-absorbing cleaning belts arranged on both sides of the transport belt and brought into contact with the transport belt in accordance with a signal triggered by the sensors. For cleaning the transport belt, the cleaning belts are wetted on their rear faces with an ink cleaning fluid and moved against the transport direction of the transport belt.
European patent 0 269 602 B1 issued Jan. 2, 1992, describes a method for drying of printed materials web in which the latter are fixed in non-slip form on a transport belt, passed with the transport belt in a straight line through the dryer and then lifted off the transport belt. Thus, a material web screen-printed using printing ink can be lifted off the transport belt without smudging. The belt is then subjected to wet cleaning by means of a belt washing apparatus, said apparatus being followed by a water-squeezing device for removing the water quantity carried by the transport belt. For complete drying of the transport belt, the latter is passed through a dryer so that the belt can subsequently receive the material web again.
The disadvantage of the apparatuses described is that cleaning fluids are used for removing residual dye or ink on the transport belt and have to be removed again from the band by correspondingly expensive equipment. In addition, the transport belt must then be subjected to drying before a new printing material can be placed on it or supplied to it.
A particular drawback of European patent application 0 744 301 A1 is that the ink-wetted transport belt is first passed through the microwave dryer, which makes cleaning more difficult. This cleaning method also has the effectxe2x80x94due to the necessary friction between the cleaning belts and the transport beltxe2x80x94of increasing wear. In particular, high speeds of the transport belt cannot be achieved for printing of the printing materials, since otherwise cleaning the dried-on ink off the belt would not be assured.
The object underlying the present invention is to provide a method and apparatus for cleaning an endless transport belt from the excess ink output from an inkjet printer, with ink adhering to the transport belt being completely removable and collected while retaining a high transport belt speed.
In accordance with the invention, in a method for cleaning an endless transport belt from excess ink ejected by an inkjet printer, where upstream the outer surface is guided horizontally for printing a printing material by means of an inkjet print head, and downstream after printing and removal of the printing material the transport belt is deflected over a roller and conveyed to a cleaning apparatus, cleaning is performed by application of a converging compressed-air stream onto the outer surface of the ink-wetted transport belt by means of an air conduit, said conduit comprising a suction nozzle, and by extraction of the ink/air mixture produced using the suction nozzle, the application and extraction of the air stream being simultaneous. The convergence of the compressed air stream is produced by an outlet opening of the air conduit of the pressure nozzle, said opening being inclined peripherally relative to the suction nozzle. In particular it is achieved advantageously that in view of a high air stream directed to the suction nozzle on all sides, ink can only be separated and removed from the transport belt by air, with the drying of the transport belt being effected simultaneously and supported by the specially coated surface of the transport belt. As a result of the selected pressure parameters of the nozzles, where the magnitude of negative pressure exceeds that of the gauge pressure, spraying of the ink/air mixture into the surroundings of the transport belt is prevented, in particular by the fact that the compressed-air stream is applied at right angles to the transport direction of the transport belt over the entire transport belt width of the outer surface. Sensors used for detecting ink residues on the transport belt are also no longer necessary.
In the apparatus for cleaning the outer surface of an endless transport belt from ink ejected from an inkjet printer not for printing purposes, said apparatus being arranged in the transport path of the transport belt of an inkjet printer, a pressure nozzle is used for application of compressed air to the outer surface of the ink-wetted transport belt, said pressure nozzle being formed by a suction nozzle arranged centrally in the pressure nozzle for extraction of the ink/air mixture produced by the compressed air.